Side shiftable carriage assemblies for lift masts have been utilized for decades to enable the operator of a material handling vehicle upon which the lift mast is mounted to be able to move a load or position the carriage transversely relative to the lift mast without moving the vehicle. Such a feature facilitates ease of operation for the operator and increases the speed of the loading cycle with reduced operator effort. A typical side shift carriage, such as shown in U.S. Pat. No. 4,392,773 dated Jul. 12, 1983, to Richard J. Johannason utilizes a fluid operated jack for shifting the side shift frame transversely relative to the spaced apart uprights of the lift mast. Typically, the side shift jack is located in the window defined by the rectangular structure of the side shift frame. Placing the side shift jack at such a location, at times during operation of the carriage and lift mast, may reduce the vehicle operator's ability to carefully position the carriage relative to a load to be lifted. This reduction in ability may occur during both elevational and transverse movement of the side shiftable carriage frame.
Many attempts have been made to improve visibility through the carriage and side shift carriage frames. One such attempt is shown in Offenlegungsschrift 2,716,704 to Otmar Kaup which published on Oct. 19, 1978. The Kaup reference teaches the placement of a pair of axially aligned side shift jacks which are mounted on a support plate anchored to the carriage frame. The forks are slidably supported on the cylindrical housings of the jacks by a pair of guide members. Actuation of the jacks of Kaup moves a support member connected to the guide members and causes the forks to translate along the cylinders in a side shiftable manner. Due to this construction, the weight of the forks and any load on the forks is passed radially through the cylinders and the cylinder rods. This causes deflection, distortion, and bending of the cylinders and their rods which ultimately results in fluid leakage and premature failure. The support plate connecting the cylinders together adds undesirable bulk to the apparatus which reduces the maximum amount of visibility of the vehicle operator.
Because the cylinders of Kaup are permanently attached to the support plate, the potential for removing, repairing and replacing an individual jacks is prevented. Thus, if one jack requires repair or replacement, both jacks and the support plate connecting the jacks together would have to be replaced. Further, because the individual guide members are mounted on the cylindrical housings, a high quality cylindrical steel housing with a good quality finish is required. This is necessary in order to achieve smooth sliding motion of the forks. Since the forks are transversely offset from the support guide members, any load placed on the forks will tend to cock the forks in a plane of the jack axis. The additional moment of force acting on the cylinders will increase the bending loads on the jacks and thus cause premature wear and failure of the jacks and associated components.
Since the Kaup patent does not have a side shiftable frame mounted on the carriage frame, the potential for early hour failures is great. This is primarily due to the fact that the guide length of the support guide members is relatively short compared to the long length of guide provided on a typical side shiftable frame such as shown in Johannason.
In view of the above, it is desirable to provide a side shiftable carriage assembly which has good visibility, compact construction, and good load resisting characteristics. It is also desirable to provide a side shiftable carriage assembly that is durable but easily serviced and disassembled. To achieve this, it is necessary to provide ease of removal and installation of the shift jacks thereon.
The present invention is directed to overcoming one or more of the problems as set forth above.